{b₂-b₁=18
{b₄-b₃=162
{b₁q-b₁=18
{b₁q³-b₁q²=162
{b₁(q-1)=18
{b₁q²(q-1)=162
{b₁=18/(q-1)
{(18/(q-1))*q²(q-1)=162 => 18q²=162
q²=9
q₁=3 q₂=-3
при q₁=3 b₁=18/(q₁-1)=18/(3-1)=18/2=9
при q₂=-3 b₁=18/(q₂-1)=18/(-3-1)=18/(-4)=-4,5
(bn) 9;27;81;... и (bn) -4,5;13,5;-40,5;...